I lvled my Assassin straight from 10-42 now with darkness from the start.
I had no issues at all, I was kind of surprised about it actualy. My DPS seemed comparable to my PTs wich I lvl Pyrotech so DPS was awsome for the fact I was tank specced and in full tank gear aswell.
I had Khem suited in DPS stance and gear with taunts turned on so he could offtank a bit. Replaced him with Andronikus when I got him and Andronikus with Ashara tho. Works like a charm downtime isnt that bad either once you get Harnessed Darkness for some more self healing. Been thinking about using Talos once I get him wich is soon. But Ill see when I get there.
So from my experience I realy enjoyed playing and lvling as a tank (even tho I was realy scared it might suck big time :P) Havent tried Deception yet will do once I hit 50 for pvp.
Id say hang in there tbh but if you realy find it so boring wait until you ding 35+ and can start getting points in Harnessed Darkness.
And the fact that you get GF queue pops almost instantly as you sign is just a small but imo big bonus
PS: I didnt feel squishy at all tbh and I tanked all FPs so far maybe youre healers sucked ?